20 May 2010

Last Word on Malaria?

[UPDATE: In the BBC the lead author of the Nature study has this to say:

"I'd say what we've shown is that if we can provide people with existing technologies such as drugs and bednets, we have the capacity as a global community to reduce the misery this disease causes. Climate change is, in our view, an unwelcome distraction from the main issues."]

Our findings have two key and often ignored implications with respect to climate change and malaria. First, widespread claims that rising mean temperatures have already led to increases in worldwide malaria morbidity and mortality are largely at odds with observed decreasing global trends in both its endemicity and geographic extent. Second, the proposed future effects of rising temperatures on endemicity are at least one order of magnitude smaller than changes observed since about 1900 and up to two orders of magnitude smaller than those that can be achieved by the effective scale-up of key control measures. Predictions of an intensification of malaria in a warmer world, based on extrapolated empirical relationships or biological mechanisms, must be set against a context of a century of warming that has seen marked global declines in the disease and a substantial weakening of the global correlation between malaria endemicity and climate.

On the surface, the connection between malaria and climate change is intuitive: higher temperatures are known to boost mosquito populations and the frequency with which they bite. And more mosquito bites mean more malaria.

Yet when epidemiologists Peter Gething and Simon Hay of the Malaria Atlas Project at the University of Oxford, UK, and their colleagues compiled data on the incidence of malaria in 1900 and 2007 (see page 342), they found the opposite: despite rising temperatures during the twentieth century, malaria has lost ground. According to the models the researchers used to tease out the factors affecting the incidence of malaria, the impact of public-health measures such as improved medications, widespread insecticide use and bed nets have overwhelmed the influence of climate change. "Malaria is still a huge problem," says Gething. "But climate change per se is not something that should be central to the discussion. The risks have been overstated."

Some earlier analyses painted a dire picture of a malaria-ridden future, but these models often exclusively evaluated the impact of warmer temperatures without taking other factors into consideration, says Paul Reiter, an entomologist at the Pasteur Institute in Paris. The latest assessment of the Intergovernmental Panel on Climate Change noted these concerns: "Despite the known causal links between climate and malaria transmission dynamics, there is still much uncertainty about the potential impact of climate change on malaria at local and global scales."

The Nature News article ends on a predictable note, quoting a researcher who says:

"This does not diminish the importance of climate change at all."

I agree with this statement of course, because I never thought addressing malaria was a key justification for dealing with climate change in the first place. However the systematic overselling of malaria and climate change in the past requires some attention, and it is not the only context in which these dynamics have occurred -- disasters and climate change provides another obvious example.

Hopefully, the new study will mark a new era in the climate debate where it is accepted among the mainstream scientific community to raise challenges to unsupportable claims made to support action, rather than seeing them go unquestioned because of the perceived delicate politics of the climate issue. In this spirit, I see that Andy Revkin, who also discusses the paper, pokes a little fun at one such serial exaggerator.